The field of the invention is manufacturing of semiconductor micro-electronic devices.
Micro-electronic devices are used in a wide range of electronic products. These devices are typically manufactured from semiconductor (most often silicon) wafers. Using photolithography techniques, thousands of discrete electronic components, such as transistors, can be manufactured on a single silicon chip, with many silicon chips produced from a single wafer. The components on the chip, and the interconnections (or wiring) between them are formed in part with a metal, most often aluminum. However, recently, the semiconductor industry has moved towards using copper in place of aluminum, as copper provides several advantages. Consequently, copper metalization techniques are currently being actively researched.
Manufacturing of semiconductor devices with copper requires several critical cleaning steps. The first, a chemical-mechanical polishing step, is required after the copper interconnections or wiring have been formed, with an inlay process. This step uses a polishing slurry. When this polishing step is completed, the copper surfaces are contaminated with residual polishing slurry. The slurry must be removed from both the copper surfaces and the oxide surfaces.
A second cleaning step is required after the via etching step. Residues are left in the via hole after the plasma etching step, and must be removed.
In the past, strong alkaline solutions have been successfully used, with aluminum surfaces on semiconductor devices, to remove slurry after polishing steps, and also to remove residue in via holes after plasma etching. However, with semiconductor devices using copper, strong alkaline solutions are unacceptable and have not been used, because these solutions have an excessive etch rate on the copper, relative to the surrounding dielectric film. In addition, strong alkaline solutions form hydroxide film on the copper surface.
Accordingly, there is a need in the semiconductor industry for improved techniques for cleaning copper surfaces.
To this end, a method for cleaning a copper surface of a semiconductor device includes the steps of purging the environment around the copper surfaces using nitrogen gas. The alkaline solution is then applied to the copper surface within the nitrogen environment. As oxygen is displaced, the copper etch rate is greatly reduced, and the shiny metallic copper surface is not degraded.
In a second separate aspect of the invention, nitrogen is introduced into the alkaline solution, to remove oxygen from the solution, thereby reducing the oxidation potential of the solution.
In a third aspect of the invention, the alkaline solution is heated to 60-85xc2x0 C.
Other and further objects and advantages will appear hereinafter.